1. Field of the Invention
The present invention relates to novel ablation-transfer imaging media comprising a support substrate having an image radiation-ablative topcoat essentially coextensive therewith, the imaging radiation-ablative topcoat including an ablation sensitizer and an imaging amount of a non-ablation sensitizing contract imaging material container therein. This invention also relates to a transfer method/system for simultaneously creating and transferring a contrasting pattern of intelligence on and from such ablation-transfer imaging media to a receptor element in contiguous registration therewith, whereby said imaging material delineates said pattern of intelligence thereon. The pattern of intelligence transferred to the receptor element is thus of opposite sign of that simultaneously created on the imaging medium.
The present invention especially relates to photo-induced ablation-transfer imaging/recording and, preferably, to laser-induced ablation-transfer imaging/recording particular adopted for such applications as color printing/proofing and masking.
2. Description of the Prior Art
The phenomenon of, e.g., laser-induced ablation-transfer imaging, is generically known to this art and is believed to entail both complex non-equilibrium physical and chemical mechanisms. Indeed, such laser-induced ablation-transfer is thought to be effected by the rapid and transient accumulation of pressure beneath and/or within a mass transfer layer initiated by imagewise irradiation. Transient pressure accumulation can be attributed to one or more of the following factors: rapid gas formation via chemical decomposition and/or rapid heating of trapped gases, evaporation, photo and thermal expansion, ionization and/or by propagation of a shockwave. The force produced by the release of such pressure is preferably sufficient to cause transfer of the imaging layer to an adjacent receptor element. The force is preferably sufficient to effect the complete transfer of the exposed area of an entire layer rather than the partial or selective transfer of components thereof.
Other material transfer imaging/recording techniques based on equilibrium physical changes in the material are also known to this art, but are limited in terms of both the overall speed of the process as well as in the materials which can be employed therefor. In particular, ablation transfer differs from known material transfer techniques such as, for example, thermal melt transfer and dye sublimation/dye diffusion thermal transfer (D2T2). Each of these prior art techniques typically employs thermal print heads as the source of imaging energy.
Alternatively, it is known to employ laser heating in lieu of the thermal printing head. In these systems, the donor sheet includes a material which strongly absorbs at the wavelength of the laser emission. In the thermal melt transfer process, when the donor sheet is irradiated, this absorbing material converts the laser light to thermal energy and transfers the heat to a colorant transfer layer which also includes a binder, fusible compound, etc., thereby raising its temperature above its melting point to effect its transfer onto an adjacent receptor sheet. In the D2T2 process, only the colorant is transferred to a specially treated or special receptor sheet (e.g., coated or porous) by sublimation or thermal diffusion. See, for example, JP 62/140,884, UK Patent Application GB 2,083,726 and U.S. Pat. Nos. 4,804,975, 4,804,977, 4,876,235, 4,753,923 and 4,912,083.
Compare also U.S. Pat. No. 3,745,586 relating to the use of laser energy to selectively irradiate the uncoated surface of a thin film element, coated on one side with a contrast imaging absorber, to vaporize and to cause the selective transfer of the absorber coating to an adjacently spaced receptor, and U.S. Pat. No. 3,978,247 relating to sublimation transfer recording via laser energy (laser addressed D2T2), wherein the contrast imaging material is also the absorber.
Nonetheless, these processes are limited in a variety of significant respects. For example, in melt transfer, the composition must contain low melting materials to transfer a pigment or dye and receptor sheets appropriately textured for wicking or having special coatings are required for best results. In D2T2, only the imaging dye itself is transferred; thus, it becomes necessary to employ special receptor sheets in order to effectively bind and stabilize ("trap") the dye. Compare, for example, U.S. Pat. No. 4,914,078 to Hann et al. Furthermore, additional post-heating treatment steps, such as the "setting" of the dyes in the binder which is present on the receptor sheet increases both the complexity and the time associated with the process. Such process is also limited to those dyes and pigments which undergo sublimation or diffusion in response to the particular imaging stimulus.
These processes are further limited in that the relatively slow processes of heat diffusion and thermal equilibrium are involved.
Accordingly, need exists in this art for a transfer process which is far more rapid that current transfer techniques, which can effectively employ a wide variety of contrast materials and which is not limited to specially treated or special receptor elements.
Laser-induced recording based on the removal or displacement of material from the exposed area is also known to the recording art. However, these applications do not require transfer of material from one substrate to another. Historically, laser-induced recording has been used, for example, in optical disk writing with near infrared (IR) lasers typically emitting at wavelengths ranging from 760 nm to 850 nm employed as the writing source. Since polymeric binders are typically non-absorbent in the near infrared region (760 nm to 2500 nm), infrared absorbers, i.e., sensitizers, are added to the binders to absorb the laser radiation. This arrangement allows the laser radiation absorbed by the sensitizer to be converted to heat which causes pit formation. See, for example, U.S. Pat. Nos. 4,415,621, 4,446,233, 4,582,776 and 4,809,022 and N. Shimadzu et al., The Journal of Imaging Technology, Vol. 15, No. 1, pg. 19 (1989). However, because this technology does not entail the imagewise transfer of materials from one substrate to another, these systems will not be further discussed.
These also exist in the recording art instances of laser-induced ablative transfer imaging entailing the displacement of material from a donor medium and adherently transferring same to an adjacent receptor element. These are limited to the use of large amounts of a black body absorber such as graphite or carbon black in conjunction with a Nd:YAG laser emitting at 1064 nm to transfer a black image. See, for example, U.S. Pat. Nos. 4,245,003, 4,702,958 and 4,711,834 (graphite sensitizer/absorber), U.S. Pat. No. 4,588,674 (carbon black sensitizer/absorber), and Great Britain Patent No. 2,176,018A (small amounts of Cyasorb IR 165,126 or 99 in combination with graphite as the sensitizer/absorber).
To produce these particular imaging media, the sensitizers/absorbers are usually dispersed in commercially available binders and coated onto a laser transparent support. The binders include both self-oxidizing binders, e.g., nitrocellulose, as well as non-self oxidizing binders such as, for example, ethylcellulose, acrylic resins, polymethylmethacrylate, polystyrene, phenolic resins, polyvinylidene chloride, vinyl chloride/vinyl acetate copolymers, cellulosic esters and the like. Since the black body absorbers employed are highly absorbent in the visible and ultraviolet (UV) as well as in the infrared region, the resulting transferred image is always black due to the presence of the absorber. Such ablative transfer imaging based on black body absorbers is therefore entirely ineffective and wholly unsuited for many applications, e.g., color transfer, imaging, color proofing, invisible security printing, etc.
Thus, serious need continues to exist in this art for a photo-induced ablative transfer imaging medium that can be sensitized independently of the contrast imaging material(s) and is therefore not limited to contrast materials which must absorb the imaging radiation. Like need exists for an ablative transfer imaging medium that may be sensitized to absorb visible and/or near IR light.
In particular, existing desiderata in this art include:
1. Media that can be employed in the photo-induced ablative transfer process to provide full color images faster than possible using current melt or sublimation techniques and that can be tailored to meet a wide variety of specifications for color imaging. PA1 2. Media that can be employed in a photo-induced ablative transfer process to produce masks which selectively block the light from exposure units employed in pre-press production in the graphic arts and printed circuit industries. PA1 3. Media that can be employed in a photo-induced ablative transfer process to produce substantially colorless fluorescent images, e.g., for the security marking of documents.